This work proposes to attempt to purify and characterize the nuclear acidic protein antigen (PM-1). The PM-1 antibody has been shown to have a high specificity for patients with polymyositis and polymyositis-scleroderma overlaps. It is hoped that with purification and characterization of the antigen we can then develop more sensitive tests for detection of the antibody. The long-term objective of this study is to examine the immune reactivity to the PM-1 antigen and its relationship to the pathogenesis of polymyositis and dermatomyositis.